There is a thread somewhere (I think) where
@johnk_10 compares the STL and the SVT. It was probably YEARS ago when the STL first came out. I think he gives some "SVT Settings."
There are over 10K posts in the main Streamliner thread... and several other threads, so might take some searching to find it... or maybe someone will chime in.
But yes... big clean tube amp - thats why I use it. WA with more power, Dual Showman sounds, SVT etc... I think the STL is very heavily influenced by the Sadowsky SA200... which seems to have a pretty good reputation.
As far as power, there are those that say they have the STL 600 and have never wanted for more power. I have a 900 - because that was what was FS at the time. My impression is that the 600 would have plenty of headroom for "clean, punchy, and warm."